Gravid spider

We had just an afternoon for our usual Saturday walk, so we did a circuit from home - over Kinnoull and Deuchny Hills, along  Coronation Road and back along Milkboys Walk. (Coronation Road is the old route from the Tay across to Scone, used by Scottish kings travelling from Falkland Palace to be crowned at the Stone of Scone. It's mostly a narrow track now.)

On the way, Mrs P spotted this spider. She wasn't keen to be photographed, and it was only looking at the picture afterwards that I saw the egg sac. Is it a grass spider?